mmmmm food for thought!
However, past experience is that communities don't tend to mix and tbh the white English young people i know are out working worldwide as they always did, i'm not a fan of the belief English youth are somehow lazy and need to be shown how to work...
Again another presumption, there is no evidence the UKs trade will increase significantly with the RoW, other countries inc the EU are also after this trade!! we aren't the only ones.
Brexit, as far as i can see, was exactly what you say you don't want, closing the door to Europe, island nation, inward looking.
The UK had a huge voice in the EU, very influential, our defence forces, science and our net contribution saw to that, now, the EU will evolve without us... the EU is in the top 3 of world science and technology blocs, it will form and grow existing relationships with China/Asia & the USA... the pity is, as you say, the UK IS a small island nation and will have very little to offer on its own.
We could mitigate that by joining Horizon and other EU science projects but not looking like Sunak is interested.